Standard CIE Research Articles

Strong donor-acceptor interaction of difluoroboron β-diketonates with polyvinylcarbazole: Deeply red-shifted emission of charge-transfer complexes and exciplexes

Donor-acceptor systems exhibiting exciplex luminescence attract much attention due to the wide prospects for their application in the field of OLEDs, nonlinear optics and lasers. Difluoroboron β-diketonates (BF2bdks) are a well-known class of organic dyes, which are able to form effective exciplex fluorescence, but this process has not received due attention for practical application. Strong donor-acceptor interaction in polyvinylcarbazole (donor) and BF2bdks derivatives (acceptor) binary system induces deeply red-shifted emission of charge-transfer complexes and exciplexes with a large bathochromic shift up to ∼170 nm relative to conventional monomeric luminescence. The results of quantum chemistry simulation are in agreement with the experiment data. Luminescence color tuning of the film are capable by the dye concentration, the donor-acceptor properties of the dye substituents and even the excitation wavelength. White light broad spectrum of a dual luminescence of the investigated binary systems has CIE chromaticity coordinates (0.35; 0.33) close to the standard neutral white light CIE coordinates (0.33; 0.33). This study will facilitate photophysical research and industrial applications of donor-acceptor binary systems based on polymer materials.

Deterministic rendering of structural color induced by atypical nano-gratings in ultra-precision diamond cutting

Ultra-precision diamond cutting (UPC) has been recently proposed for fast generation of nano-gratings to render diffractive structural color on various metallic surfaces. However, the complex nanoscale generation mechanism and atypical grating topography provide the significant challenges for deterministic rendering of structural color with standard representations. In this paper, an innovative diffraction prediction model is firstly proposed to describe the diffractive spectrum of atypical gratings under the full considerations of cutting process parameters, double working facets, material optical properties and environmental conditions. The standard CIE 1931 chromaticity diagram for grating-induced structural color is released for color gamut determination and optimization, where the color gamut range is defined by a novel concept of average saturation. The experimental results demonstrate the deterministic generation of three groups of nano-gratings with desired 3D topography, of which the measured angle-dependent diffractive spectrum and rendering color attributes show good agreements with theoretical results. Moreover, the new topography-modulation based strategies for achieving maximal color gamut and manipulating the ternary color attributes are clarified. The outcome of this paper lays the scientific foundations for deterministic rendering and performance enhancement of structural color enabled by UPC processes.

Perceived glare from the sun behind tinted glazing: Comparing blue vs. color-neutral tints

While the influence of a glare source's spectrum on sensitivity to discomfort glare has been demonstrated repeatedly under electric light conditions, it has not yet been studied under actual daylit conditions. To investigate the influence of spectral alterations of the sun disc on glare perception when seen behind a colored glazing, we performed a cross-evaluation of occupants' visual comfort in a space either daylit through blue-tinted electrochromic (EC) glazing (20 participants) or through color-neutral glazing (55 participants), having selected two types of glazing that are widely employed in commercial buildings. Under both types of glazing, participants experienced four glare scenarios presenting different glazing transmittances (from low to extremely low) in which the sun was the only glare source visible. Comparing the participants' responses to glare, we found that participants experienced discomfort more often in blue-tinted glazing compared to color-neutral glazing, even though glare metrics would have predicted higher levels of discomfort in these latter cases. This indicates that participants basically tolerated glare better under color-neutral daylit conditions compared to blue-colored conditions. To explain our findings, we considered four spectral discomfort glare sensitivity functions that have previously been proposed to replace the standard CIE V2°(λ) and applied them to the DGP and CGI glare metrics. However, none of these adjustments to glare metrics made any difference to our findings, which consistently showed an increased glare sensitivity under shorter wavelengths, indicating that its cause should be sought elsewhere. Some hypotheses are formulated at the end of the paper in this regard.

Whiteness Perception under LED Source with High Content of UV Radiation

Whiteness is an attribute of color perception with high brightness and low colorfulness. In this study, the correlation between instrumental measurement and visual assessment of whiteness of 40 optically brightened white samples was investigated under a LED light source of correlated color temperature (CCT) 5000K combined with Wood's UV-A lamp. Due to over exposure of UV radiation, tested samples were outside of CIE limit. In those cases, standard CIE whiteness formula show significant shift in whiteness interval scale. A high correlation was identified between visual assessment and modified Vik-Viková whiteness formula. The investigations have also shown that the existing CIBA plastic whiteness scale needs to be expanded.

Window-to-Wall Ratio as a Mode of Daylight Optimization for an Educational Building with Opaque Double-Skin Façade

This study investigates the impact of Window-to-Wall Ratio (WWR) and Shading Coefficients (SC) as passive design strategies to optimise daylight in an opaque brick Double-Skin Façade (DSF) of an education building in Depok, Indonesia. A sample education building was simulated with DiaLux software for calculating the daylight distribution due to WWR on a daily basis during normal office hours. The optimum amount of window size and glazing were investigated for a typical floor plate area of 315.16m2. WWR was considered from 30% to 60% at 10% intervals in a horizontal and vertical expanding method of window. The simulations were performed in two sky conditions (sunny sky and standard CIE overcast sky) on different dates using glazing material of different SC. The primary findings of this study are that 40% WWR with SC 0.42 and 60% WWR with SC 0.95 achieve the best results for the north and south façade respectively of a DSF building.

Theoretical Impact of Building Façade Thickness on Daylight Metrics and Lighting Energy Demand in Buildings: A Case Study of the Tropics

In daylighting design, variation of building façade thickness (f) will result in variation of the daylight opening areas, which in turn will modify the values of daylight metrics within the space. However, studies dedicated to investigating the impact of varying f on indoor daylight metrics are relatively scarce. This study, therefore, aims to assess the theoretical impact of various façade thicknesses on various daylight metrics and lighting energy demands in a reference office space. Analytical calculations are performed using an outdoor diffuse illuminance profile of a tropical city. The building façade thickness values are varied within 0–0.50 m, at window-to-wall ratios (WWR) of 25%, 50%, and 75%. Based on sensitivity analysis, it is found that variation of f yields different impacts on the observed metrics, with sDA300/50% being the least influenced. Among all metrics in the central calculation point, DA300, UDI-a, and UDI-a′ yield relatively small coefficients of variation, and thus, have the lowest uncertainty with respect to f. Among all metrics for the entire room, sDA300/50% and sUDI-a50% have the lowest uncertainty, with interquartile ranges of no more than 0.4%. Overall, the contribution of this study is providing insight into the impact of façade thickness on various daylight metrics in indoor spaces, particularly in the worst-case scenario under the standard CIE overcast sky.

Methods to improve colour mismatch between displays

With the rapid development of display technology, the colour mismatch of the colours having same tristimulus values between devices is an urgent problem to be solved. This is related to the wellknown problem of observer metamerism, caused by the spectral power distribution (SPD) of primaries and the difference between individual observers' and the standard CIE colour matching functions. An experiment was carried out for 20 observers to perform colour matching of colour stimuli with a field-of-view of 4° between 5 displays, including two LCD and two OLED, against a reference LCD display. The results were used to derive a matrixbased colour correction method. The method was derived from colorimetric visually matched colorimetric data. Furthermore, different colour matching functions were evaluated to predict the degree of observer metamerism. The results showed that the correction method gave satisfactory results. Finally, it was found that the use of 2006 2° colour matching function outperformed 1931 2° CMFs with a large margin, most marked between an OLED and an LCD display.

Cool white light emission from Dy3+-doped SiO2 – Bi2O3 – Ga2O3 – B2O3 -GeO2- TeO2 glasses: Structural and spectroscopic properties

The authors aim to study multi former oxide glasses doped with different concentrations of Dy3+ (0.00, 0.5, 1.0, 1.5, and 2 mol%) for white light-emitting application. All samples characterized by XRD, FTIR, and optical properties (absorption, excitation, and emission). The optical band gap calculated by a differential method. FTIR spectra confirm the network composed of GaO4, GeO4, TeO4, and BO4 tetrahedra, BO3 triangles, B-O-B linkages, and SiO4 tetrahedra with one NBO. In addition to the TeO3, BiO3, TeO6, and BiO6 vibration groups.Oscillator strengths and Judd–Ofelt parameters (Ω2, Ω4, Ω6) calculated and found that the glass samples had a variable trend from Ω2 > Ω4 > Ω6 to Ω2 > Ω6 > Ω4, at a Dy2O3 content >1 mol%. Furthermore, radiative emission transition probability (AR), branching ratio (βR), and radiative lifetime (τR) estimated for Dy3+ ion in various excited states using J–O parameters. Upon 454 nm excitation, 4F9/2 → 6H15/2 [483 nm (blue)], 4F9/2 → 6H13/2 [575 nm (yellow)], and 4F9/2 → 6H11/2 [680 nm (red)] emission. Among them, it noticed that the transition 4F9/2 → 6H13/2 shows the highest intensity.The CIE chromaticity coordinates, correlated color temperature (CCT), and color purity (CP) indicate a generally neutral white light emission from all samples, which meant their suitability for optical applications. Determination of the white light coordinated from the CIE program, which verifies the values of samples are close to the pure white light. And sample containing 2 mol% Dy3+ close to the standard CIE D65 glow.

Visual Perception in External Lighting Conditions

LED street lighting is a topical trend in modern outdoor lighting. High light output of LEDs creates all conditions for modernization of electric lighting networks in Ukraine. Human vision is a complex process associated with retinal light perception. Vision is divided into: day vision, night vision, and twilight vision. The function of the eye is highly dependent on the distribution of brightness in the field of vision. The spectral sensitivity of photoreceptors varies for different wavelengths of the visible spectrum and different levels of light intensity. The rationing of the lighting installation is based on detailed studies of the observer’s visual performance depending on different lighting conditions. One of the main luminous parameters that can easily be measured objectively is illumination. Brightness as a function of illumination, the observer’s position and the spectral coefficient of the working surface reflection is more informative, but has some difficulty in measuring. There is a clear need to develop a system that would make it possible to uniquely assess the visual efficiency of a given spectral composition under certain observation conditions. It was decided to introduce the term equivalent brightness as the parameter of such a system. The difficulty of using the function Vek(λ,Lek) to calculate the equivalent brightness is the function’s dependence Vek(λ,Lek) on Lek. The aim of the study is to approximate the function of the relative spectral luminous efficiency in mesopathic regions by a set of standard CIE functions that do not depend on the value of equivalent luminosity. The calculation method Vek(λ,Lek) is proposed using only two normalized functions of the relative spectral radiation efficiency for day V(λ) and night V'(λ) vision. The use of such approximation function makes it possible to determine the equivalent brightness, which adequately reflects the level of visual perception under the conditions of ambient illumination, based on the photometric brightness of the light source. To calculate Vek(λ,Lek) we use the ICE recommended functions of relative spectral light efficiency for the twilight vision, which are based on the spectral composition of the blackbody radiation with a color temperature of 2042 K. The use of the developed methodology provides results that more accurately characterize the efficiency of light sources in outdoor lighting installations compared to the results of calculations obtained when using standard methods.

White-emission from ZnS:Eu incorporated in AC-driven electroluminescent devices via ultrasonic spray pyrolysis

In this work, white-emitting-alternating-current-thin film electroluminescent (w-ACTFEL) devices are demonstrated using europium-doped zinc sulfide (ZnS:Eu) and zirconium oxide (ZrO2) as the emissive and dielectric layers, respectively. These films were deposited by the ultrasonic spray pyrolysis technique on antimony-doped tin oxide glass substrates, forming a standard metal-insulator-semiconductor-insulator-metal (MISIM) architecture. 10 kHz sinusoidal voltages activated the white-EL of the devices. The colorimetric characteristics were investigated for three amplitudes of the applied voltage. The emission of the devices is made up of wide and narrow bands with peaks corresponding to violet, blue, green and red light, which together produce the resulting white light. According to the colorimetric analysis, this white light is close to the standard D65 CIE illuminant with a minimal dominant blue component. The variation in voltage amplitude induces small changes in the visual characteristics of the EL emission. The white-EL emission of these MISIM devices is attributed to the electron-impact excitation and subsequent relaxation of the excited levels of Eu2+ and Eu3+ impurities, and defect levels in the sublayer regions adjacent to the ZrO2–ZnS:Eu interfaces.

Preview the Products on Display at Display Week 2021

Preview the Products on Display at Display Week 2021

Fabrication and optical properties of high-quality blue-emitting CsPbBr3 QDs-PMMA films

Abstract The blue-emitting CsPbBr3 quantum dots (QDs) have currently received widespread attention due to high photoluminescence quantum yields (PLQYs), but their instability mainly caused by self-aggregation or environmental erosion (i.e. moisture and oxygen) should be solved to gain more progress in further application. This paper presented a feasible approach to high-quality blue-emitting CsPbBr3 QDs-polymethylmethacrylate (PMMA) films, in which PMMA provided a solid framework to protect CsPbBr3 QDs by the chelation between C O and Pb2+ ions, thus resulting in the stability of CsPbBr3 QDs. The CsPbBr3 QDs-PMMA films exhibited remarkable properties including water resistance, flexibility, deep-blue emission (465 nm), and comparatively high PLQY (45%). The blue LED fabricated by the films displayed a CIE coordinate (0.14, 0.10), which was corresponding to the standard blue CIE coordinate (0.14, 0.08) according to National Television System Committee (NTSC).

Relationships between habitat quality and ecological properties across Ziarat Basin in northern Iran

This study aimed to examine the relationships between habitat quality and ecological properties including land use, elevation, slope, and soil parameters (SOC, phosphorus, and color parameters in the standard CIE L*a*b* color system), across the Ziarat Basin of the Gharehsoo River in northern Iran. Data from satellite imagery, field sampling, and previous reports were used to quantify habitat quality using InVEST, while soil properties were mapped using the IDW method. The relationships between all criteria were assessed using the ArcGIS Geostatistical Analyst and Pearson’s correlation coefficient. The impact of land use on habitat quality was also evaluated based on a subset of landscape metrics including NP, PD, LPI, LSI, and PCI. The results demonstrated that the southern habitats had higher quality than the northern parts of the basin. Habitat quality had a significant positive relationship with elevation (R = 0.9), slope (R = 0.77), SOC (R = 0.65), and a* parameter (R = 0.57), whereas it had a significant inverse relationship with phosphorus (R = − 0.61) and L* parameter (R = − 0.84). Moreover, elevation and slope had a significant positive correlation with SOC (R > 0.53) and a* parameter (R > 0.47), and a significant negative correlation with phosphorus (R < − 0.42) and L* parameter (R < − 0.76). The analysis of landscape metrics also revealed that an enhance in the number of rangeland and forest patches increase habitat quality, whereas increasing agricultural and built-up land uses downgrade habitat quality. Conclusively, habitat quality can be correlated to landform and soil properties influenced by spatial patterns and land use types, which facilitate the understanding of ecological characteristics and land degradation.

The Lighting Environment, Its Metrology, and Non-visual Responses.

International standard CIE S 026:2018 provides lighting professionals and field researchers in chronobiology with a method to characterize light exposures with respect to non-visual photoreception and responses. This standard defines five spectral sensitivity functions that describe optical radiation for its ability to stimulate each of the five α-opic retinal photoreceptor classes that contribute to the non-visual effects of light in humans via intrinsically-photosensitive retinal ganglion cells (ipRGCs). The CIE also recently published an open-access α-opic toolbox that calculates all the quantities and ratios of the α-opic metrology in the photometric, radiometric and photon systems, based on either a measured (user-defined) spectrum or selected illuminants (A, D65, E, FL11, LED-B3) built into the toolbox. For a wide variety of ecologically-valid conditions, the melanopsin-based photoreception of ipRGCs has been shown to account for the spectral sensitivity of non-visual responses, from shifting the timing of nocturnal sleep and melatonin secretion to regulating steady-state pupil diameter. Recent findings continue to confirm that the photopigment melanopsin also plays a role in visual responses, and that melanopsin-based photoreception may have a significant influence on brightness perception and aspects of spatial vision. Although knowledge concerning the extent to which rods and cones interact with ipRGCs in driving non-visual effects is still growing, a CIE position statement recently used melanopic equivalent daylight (D65) illuminance in preliminary guidance on applying “proper light at the proper time” to manipulate non-visual responses. Further guidance on this approach is awaited from the participants of the 2nd International Workshop on Circadian and Neurophysiological Photometry (in Manchester, August 2019). The new α-opic metrology of CIE S 026 enables traceable measurements and a formal, quantitative specification of personal light exposures, photic interventions and lighting designs. Here, we apply this metrology to everyday light sources including a natural daylight time series, a range of LED lighting products and, using the toobox, to a smartphone display screen. This collection of examples suggests ways in which variations in the melanopic content of light over the day can be adopted in strategies that use light to support human health and well-being.

Impact of Color-Matching Primaries on Observer Matching: Part I – Accuracy

ABSTRACT A good color description starts with the availability of accurate color-matching functions (CMFs) or cone fundamentals (CF). Recent work indicates a discrepancy between visual metamers and those calculated using the standard CIE CMFs or other CMF sets, especially for narrowband sources. In the current study, 54 observers (varying in age, gender, ethnicity, and eye color) performed a series of achromatic color-matching experiments with a 10° stimulus using eight different narrowband primaries under an immersive, perceptually neutral (4673 K) viewing conditions. The reference stimulus was provided by a 70 cd/m2 gray (4613 K) card illuminated by a spectrally broadband light source. The results confirm that substantial and significant differences between experimental and calculated metamers exist, particularly when a short wavelength primary (404 nm) is included and especially for the CIE 1931 2° CMFs. It is found that the primary set characterized by the peak wavelengths 636 nm, 521 nm, and 447 nm, which are close to those of typical RGB primaries widely used in industry, results in the most stable matching performance across all CMF sets. Finally, in addition to the impact of primary wavelength and CMF set, the potential effect of age, gender, ethnicity, and eye color has also been investigated. The effect of age on the color matches is found to be significant and is due to differences in spectral sensitivity of young and old observers with respect to the blue primary; the impact of observer gender, ethnicity, and eye color, on color-matching accuracy is not significant.

New europium complexes and their use in red light-emitting diodes and vapoluminescent sensors

Three novel trivalent europium [Eu(III)] complexes – Eu(DBM)3Phen-Ph-Ph, Eu(DBM)3Phen-mCF3-Ph, and Eu(DBM)3Phen-pCF3-Ph – were designed, synthesized, and characterized using various spectroscopic methods. Then their photophysical characteristics were investigated. The Eu complexes in the solid phase showed a pure red emission (due to the electric dipole transitions of the Eu3+ ion). In a solution, they had multiple emissions due to their ligand contribution. The solvatochromism studies revealed that the Eu(III) complexes in the methanol and DMSO solutions had both metal ion and ligand emissions with similar intensities, which yielded a white emission. Of all the Eu(III) complexes, Eu(DBM)3Phen-mCF3-Ph showed the best quantum yield. In addition, the fluorinated mCF3 ligand had an unusually high lifetime value. Its remarkable linear decrease in luminescence intensity with increasing temperature opens a new window for its use as a sensitive temperature sensor at the 30–80°C range. The CIE color coordinates of the fabricated red LEDs (InGaN) are very close to the standard NTSC CIE color coordinates for bright red emissions, and the color purity as well as the LER values of the fabricated red LEDs are also very good. The Eu(III) complexes exhibited on-off photoluminescence switching via the vapoluminescent process and responded best to the acid-base (HCl-NH3) vapors. All these features suggest that the synthesized Eu(III) complexes are efficient candidates for red-emitting LEDs and vapoluminescent sensors. Organic chromophores, which are phenanthro-imidazole ligands based on fluorinated moieties coordinated with Eu(III) metal ions, very efficiently facilitate energy transfer from the ligand to the Eu(III) ion. The CIE color coordinates of the complexes showed a bright pure red emission, with x = 0.66 and y = 0.33 (612 nm). The fabricated light-emitting diode (LED) showed superior color quality and the complexes showed on-off-on luminescence behavior after exposure to the acid-base vapors.

Highly efficient and blue-emitting CsPbBr3 quantum dots synthesized by two-step supersaturated recrystallization

Highly efficient and blue-emitting CsPbBr3 quantum dots were successfully synthesized by two-step supersaturated recrystallization under ambient condition. This method could control the particle size within 2.8 nm, thus resulting in strong quantum confinement effect of the products. The as-synthesized CsPbBr3 quantum dots presented outstanding optical properties with highest photo-luminescence quantum yield of 87.20% and longest PL lifetime of 12.24 ns. The blue light-emitting diode made from the CsPbBr3 quantum dots exhibited a CIE coordinate (0.14, 0.10), in good agreement with the standard blue CIE coordinate (0.14, 0.08) of National Television System Committee (NTSC).

This issue of ACTA, printed and electronic

This issue of ACTA, printed and electronic

Light-chromatic identification of rare-earth luminescent fibres doped with organic onium salt

Organic onium salt has been used as a photosensitive pigment for rare-earth luminescent fibre. A certain dose of organic onium salt has been added to rare-earth strontium aluminate luminescent fibre (RESALF) during its melt spinning. It’s photochromatic property is studied by comparing RESALFs with and without the organic onium salt. RESALF photochromatic identification method is devised according to the Standard Colorimetric System CIE (International Commission on illumination) 1931 XYZ. The results show that, when excited by 365nm wavelength light, RESALF doped with organic onium salt exhibits good photochromatic properties. The luminescence color of RESALF doped with organic onium salt switches from the yellow-green region to the blue region. The light-chromatic recognition method used is thus able to provide an accurate identification of the luminescence color of the new RESALF.

An efficient nonlinear polynomial color characterization method based on interrelations of color spaces

AbstractA well‐known color characterization method is to take an image of a color chart and then to find the mapping matrix from the digital RGBs to the corresponding known CIEXYZs. However, the prediction errors are generally large in CIELAB color space because of the nonlinear transformation from CIEXYZs to CIELABs. In this article, we propose an efficient and simple nonlinear method for the color characterization of input devices. The approach for deriving a colorimetric mapping between digital RGB signals and CIELAB tristimulus values uses the polynomial modeling by considering the interrelations among the standard CIE color spaces. Furthermore, to improve the accuracy of solution, we take the polynomial root terms extension. Our algorithm is simple to implement because only a least‐squares mapping should be solved. Various computational results are given to demonstrate the efficiency and capability of the proposed method.